Mongoose Moms in Groups May Compete By Producing Larger Offspring

Group living may result in larger offspring. That is, a 13-year study from the University of Exeter has concluded that female mammals, such as humans too, may respond to competition by trying to grow larger babies. In the study, which used ultrasound for the first time to fill out findings, female mongooses were found to produce heftier pups in a response to reproductive competition.

The research results add to growing indications that social mammals might have effects on womb conditions to increase their success in reproduction. This would be yet another factor in animals' competition to increase their likelihood of having surviving offspring, along with males' antler fights and other competitions to win a mate.

"Medical and evolutionary biologists have suggested that mothers might prime their offspring during pregnancy to help them face competition after birth, but evidence for this idea remains controversial. This study provides evidence that in wild mammals, competition among mothers starts even before birth," Emma Inzani, a Master of Research student and the study's lead author, said in a release.

In the family groups of about 20 in which banded mongooses live, adult females breed each season and produce (on the same day) a pup litter. The new offspring then compete to attract food and care from the adults.

As a result of this system, mothers are unable to recognize their young in the large litter. This also keeps them from helping the pups to compete for food or attention. As a result, the mothers are left with one main recourse: sending more resources to their offspring while they are still in the womb.

"Our study is the first to use ultrasound scans to look at prenatal investment in a wild mammal, and supports the idea that mothers adjust prenatal investment in the face of competition," Inzani said in the release. Some of the details still must be worked out, though: "We don't know whether the mongooses are eating more, or might be using their stored body fat and thus trading off their current investment with future prospects," added Inzani in the release.

The study subjects were 11 groups of wild banded mongooses in Queen Elizabeth National Park in Uganda, over 13 years. Individual fetuses in ultrasound results were measured, to see how strongly each female invested her own resources in the pregnancy.

It was clear that as more females competed to reproduce at the same time, the result was that fetuses were larger for each female. In particular, this increase in the size of the fetus was most remarkable among females with low weight and when conditions were dry with little rainfall. Both factors made it all the more important for each fetus to win out over the others in the communal litter.

That said, pups that received this extra boost in the womb did not necessarily survive or grow in more impressive numbers once they were born. But there was at least one positive learning, other than offspring size: "We did find that mothers who produced the largest fetuses showed higher survival in the months after breeding, suggesting that better quality females can afford to produce larger fetuses with no consequence to their survival," Dr. Vitikainen noted in the release.